I've only messed with a couple of rifles, but I've found that a freshly cleaned and oiled barrel will throw the first shot an inch or two off (direction varies). My personal belief is that it's the oil more than anything. My opinion is that for the hunting I do it doesn't make a "killing" difference, but I'd rather throw a shot or two off after cleaning. If my rifle is not damp, I tend not to clean until I've shot a bunch of shots. If it's just a matter of sighting and practicing a few shots (like a box), I don't bother cleaning before hunging.